Method of chilling solutions



May 4, 1937.

E. PETTY ET AL METHOD OF CHILLING SOLUTIONS Filed Nov. 6, 1935 III?.

Patented May 4, 1937 2,079,182y METHon or' omLLrNo SOLUTIONS Earl Petty and Karl Finsterbusch, New York, N. Y., assignors, by mesne assignments, to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey Application November 6, 1933, Serial No. 696,"i69

6 Claims.

Our invention relates to a method of chilling solutions and more particularly to a method of chilling solutions of hydrocarbon oils in liqueed normally gaseous solvents, or mixtures oi hydrocarbon oils and liquened normally gaseous substances.

Currently inthe art of dewaxing hydrocarbon oils, it has become the practice to dilute a hydrocarbon oil with a liquefied, normally gaseous solvent and to obtain a chilling effect by evaporating a portion of the solvent to reduce the temperature of the solution. The reduction of temperature effected in this manner is governed by the physical properties of the refrigerant solvent gas and more particularly, its pressuretemperature relations. the greater the reduction in pressure the greater the expansion of the refrigerant diluent gas, resulting in a corresponding lower temperature. In dewaxing hydrocarbon oils, for example, it is frequently desired to reach temperatures as low as say minus F. in order to precipitate wax from the hydrocarbon oil. In order to obtain a favorable crystal growth and to obtain the type of crystal which will be readily iilterable, it has been found necessary to reduce the viscosity of the oil by forming a solution therewith. In the dewaxng process mentioned above, the liquefied gas is at once a solvent so that it will act as a diluent. To obtain the desired low temperature, it may be necessary in many cases to reduce the pressure to atmospheric and at times to obtain the desired evaporation by means of a partial vacuum or the imposition of subatmospheric pressure upon the solution.

vOur invention is likewise applicable to treating processes where gasolines, alcohols or naphthas are used and low temperatures are obtained by the evaporation of the normally liquid solvents by the use of sub-atmospheric pressures. In such processes, we may reduce the partial pressure according to our method and thus avoid the use of low sub-atmospheric pressures. For example; in low temperature acid treating, a def crease in temperature may be obtained by reducing the partial pressure in the treating stage by injecting lower boiling substances thereinto.

It Will be obvious that vapors prior to cooling and condensation, the' suction pressure materially affects the size of compressors and power required. Both size and power are reduced by increased suction pressure. Thus, it is more economical when recycling to receive the evaporated gas and/or vapors at higher pressure.

In a dewaxing process employing auto refrigeration, that is, cooling a liquid by evaporating a portion of the same, hydrocarbon gases of the nature of propane have been largely employed. In the practice oi dewaxing and crystallization with a propane solution, it has been found necessary to chill the solution to at least minus 30 'E'. or thereabouts, which generally requires a reduction of pressure to atmospheric 0r lower through successive stages. With the solution in equilibrium at such 10W temperatures and pressures, diiiiculties are encountered through boiling and vapor lock in transferring the liquid by pumps or other means. Accordingly, various transfer methods have been used, Such as to supercool the solution by applying vacuum to the crystallization vessel and then repressure vthe vessel by gas pressure and transfer the liqluid to storage, which is carefully insulated. The liquid may then be allowed to come to equilibrium under the effect of its own gas pressure which may be permitted to build up to approximately 5to l0 lbs. above atmospheric pressure in order that thev cool liquid may more readily be pumped to the separating apparatus.

One object of our invention is to provide a method of cooling or sub-cooling solutions or mixtures and more particularly solutions of hydrocarbon oil in a liquefied, normally gaseous solvent in which advantage is taken of Daltons law of partial pressures in order to obtain the desired evaporation and low temperature without the necessity of resorting to the use of low pressures and/or vacuum.

Another object of our invention is to provide a method of dewaxing hydrocarbon oils by the use of a liquefied, normally gaseous Asolvent in which evaporation is aided by the use of a gas and the evaporation carried out at successively reduced, equal, or increased pressures or any combination thereof. We also provide a method in which the evaporation is due entirely to the use of a gas.

Another object of our invention is to provide a method of reducing the amount of diluent that ordinarily would be required to obtain a definite cooling effect by evaporation under any given temperature-pressure conditions by the use of a gas to increase the evaporation of the diluent. For example, assume that it is necessary to evaporate 100 pounds of propane to gain a desired cooling effect, and that 1000 pounds oi propane are necessary as a diluent in order to build up suicient partial pressure to evaporate 100 pounds. By use of a gas, thus reducing partial pressure, the amount of diluent required for the evaporation of 100 pounds of propane may be reduced from 1000 pounds to, say 600 pounds.

Another object of our invention, therefore, is to reduce the overall refrigeration load since the reduction in diluent, pointed out above, reduces the total material tobe cooled and thus the amount of evaporation necessary for a given cooling effect. 'I'his reduction in diluent also reduces the amount of evaporation necessary since there is less total material to be cooled.

Crystal growth is dependent mainly on three factors, namely, time, temperature and concentration. Tne concentration has a dual aspectthe ratio of the diluent to the oil and the ratio of the diluent to the wax. It has been deiinitely established that an excess of diluent retards crystal growth. In United States Patent 1,940,014, Earl Petty discloses the method of maintaining the concentration at an advantageous point with respect to promoting crystal growth, by evaporating the diluent at a controlled rate to maintain the oil-solvent ratio, thus preventing an excess of diluent which would redissolve the precipitated wax. In United States Patent 1,940,015, Earl Petty discloses another method of preventing an excess of diluent which would interfere with favorable crystal growth by using an insulicient amount of diluent to obtain the desired low temperature solely by the evaporation of the diluent and obtaining an increment desired low temperature by a preliminary indirect heat exchange step.

Further and other objects of our invention will appear from the following description.

The accompanying drawing, which forms part of the instant specification, is a diagrammatic View of one form of apparatus capable of carrying out the process of our invention.

In general, our invention contemplates the employment of normally gaseous hydrocarbons having from 1 to 5 carbon atoms per molecule and whose molecular weight varies from 16 to 100 and having boiling ranges from minus 265 F. to plus 156 F. In selecting a gaseous mixture for the dual purpose of acting as a solvent diluent refrigerant, we find it advantageous in most cases to utilize the waste or by-product gases or vapors obtained in the processing and refining of hydrocarbon oils, or from natural gases. We may, if desired, employ a substantially pure compound within the boiling range of propane as a diluent, and use lighter gases which are not necessarily solvents as, for example, carbon dioxide, ammonia, or sulphur dioxide, or other light solvent gases, such as methane or ethane for example, as the gas tol be used for the reduction of partial pressure. In its last analysis, we inject into the cooling Zone in which a pressure reduction will permit the evaporation of a portion of the liqueed diluent gas, a lighter gas under the same pressure, in order to permit an operation of Daltons law. The result will be that a greater amount of diluent gas will be evaporated than would otherwise be accomplished unless the pressure was decreased, thus enabling a lower temperature to be reached at the desired pressure.

In the normal practice of dewaxing and crystallization by use of propane solutions, as pointed out above, low temperatures are generally required. Naturally, some of the cooling of the wax bearing oil propane solution may be accomplished by heat exchange against the chilled solution from which the wax has been removed. The remainder of the cooling is normally accomplished by autorefrigeration, i. e., evaporation of a portion of the diluent. This refrigeration is generally done in steps in which the pressure is successively reduced to permit evaporation and cooling to the desired temperature. For example, the i'irst evaporator may be held at, say, 15 to 20 pound gauge and the temperature reduced to F. by partial evaporation of propane. The chilled solution would then pass to the second evaporator where the pressure may be reduced to 3 pound gauge with attendant temperature reduction to, say, minus F. through additional evaporation of propane. second unit to the third evaporator where subatmospheric pressure would be required to further evaporate propane and reduce the temperature to, say, minus 30 F.

In our method, the solution after heat exchange is introduced into the first stage evaporator held at, say, 15 to 20 pound gauge. The evaporation of propane, under this pressure, is increased by reduction in partial pressure through the injection of a light gas, such as methane, and the temperature of the solution lowered to, say, minus 10 F. instead of 0 F. as would normally be obtained for the pressure as pointed out above. Subsequently, in the successive evaporators, temperatures of approximately minus F. and minus 30 F. are obtained by introduction of a light gas at correspondingly higher pressuresso that the final stage temperature is obtained at atmospheric or higher pressure. Naturally, combinations and sub-combinations may be developed, such as only introducing a light gas in the nal stage instead of all stages.

In our method, all evaporators may be maintained at the same pressure, the liquid being transferred to successive stages by means of pumps or preferably by the gas pressure in the evaporators and obtaining a cooling effect by evaporation of propane through partial pressure reduction by injection of light gas into each stage.'

In our method, the pressures of the evaporators may be successively increased by using pumps to transfer the liquid to successive stages and the use of a light gas to reduce partial pressure of propane in each stage and effect evaporation to obtain cooling.

It will also be noted that, in our method, cooling may be obtained in solutions that are already at equilibrium under a given4 pressure, where at these conditions no evaporation or autorefrigeration would take place, since the reduction of partial pressure by the introduction of a light gas will cause evaporation of the diluent propane.

The solution would then pass from the In general, the apparatus and process Steps offour methods,` outlined above, are similar so that, from the description of one method, others are self evident. More particularly referring to our method wherein the pressure in successive stages is reduced and to the drawing, a hydrocarbon wax bearing oil from tank I is pumped bypump 2 through lline 3 into line 4 'where it is joined by a liqueed, normallygaseous solvent which, for purposes of convenience, we will hereinafter refer to as propane, from tank 5, whence it ipasses through line 5 to line 4. The propane and oil are thoroughly mixed in an orii'ice column `1. The proportion of oil and propane may be governed by valves 8 and 9,l

and'may be in a practical example by volume 41% oil and 59% propane, which will be in the neighborhood of 57% oil by weight to 43% propane by weight.

In giving temperatures, pressures, and proportions, as we will in the following description, it is to be borne in mind that these are not' to be considered as limitations but are given only to show a practical operation'lof the process by way of example. The temperature of the mixture may be, for example, about 90 F. upon leaving the orifice column 1. The solution formed in the orice column passes through line I lto a cooler II`, which may be cooled by any suitable medium entering from pipe I2 and discharging through pipe I3. Upon leaving the heat exchanger throughline I4, the temperature of the solution will be in the nature of F. It then enters a bank of heat exchangers I5 in which the solution is passed in heat exchange with a wax free oil diluent solution, previously separated in the process. wax free oil solution will ,be about minus 35 F. effecting a considerable reduction in the temperature of the oil propane solution. The'wax free oil solution is obtained from tank I5 and is pumped by pump I1 through line I8 to the heat exchanger bank I5, from which it leaves through line I9 to pass to a pressure stabilizer 29 as will be hereinafter more fully described. The solution thus pre-cooled by indirect heat exchange, leaves the exchanger bank I5 through line 2| which terminates in a manifold portion 22 communicating with lines 23 and 24, passing to evaporator crystallizers 25 and 25 respectively. The arrangement is suchthat evaporator crystallizers 25 and 26 may be operatedin parallel, while evaporator crystallizer 21 will be in series with 4both evaporator crystallizers 25 and 26. In normal operation, however, evaporator crystallizers 25, 26, and 21 will be operated in series. The solution will pass through line 23, valves `28 and 39 being open and valve 29 being closed, into evaporator crystallizer 25. The pressure in evaporator crystallizer 25 is held below'the equilibrium pressure of the precooled solution, permitting propane to` be evaporated therefrom, through line 3I through separator 32, through line 33, valve 34 being open and valve 36 being closed; Entrained oil and/or liquid propane from the separator will return to the evaporator crystallizerd through line 31. The evaporated propane will pass through lineA 33 Vinto line 38. A light gas is present' in main`39. We will describe more fully hereinafter the cyclev through which the light gas passes. Light gas from main 39 passes through line 49, valve 4I, which is open, into evaporator crystallizer 25. f Inasmuch as the gas from main 39is oonsiderably "lighter, that is of much lower boiling The temperature of the ,exhaust main 38.

point than the diluent gas, itspresence in the chilling zone within evaporator crystallizer 25 will permit a further evaporation of propane from the solution at a given pressure',than would be obtained if the light gas were not present,

due to the operation of Daltons law of partial pressures. This additional evaporation effect, produced bythe light gas, decreases the temperature without a corresponding decrease in pressure as would otherwise be necessary if the acaation were entirely by autorefrigeration It is to be understood, however, that the light gas from line 49 may be injected into the oil-propane solution prior to its entrance into the evaporator crystallizer, The injection of light gas, whether directly into the evaporator crystallizer or into the oil-propane solution prior toits reaching the crystallizer, will have the same partial pressure efect in the operation of Daltons law Within the evaporator crystallizer.

In order to control the solution propane from propane storage tank 5 may pass through line 42 which is controlled by valve 43 into the incoming oil propane solution, through line 23. The proportion of diluent gasto the oil is of importance in determining crystal growth and the type of crystal formed so that this can be controlled by the'addition of further propane through line 42. Whenevaporator crystallizers are operated in parallel, it will be understood, of course, that Vvalve 29 will be open so that the solution may pass into evaporator crystallizers 25 and 26 simultaneously.

Continuing the' series operation, the chilled solution is withdrawn from the bottom of evaporator crystallizer 25, through line 44 which is controlled by valve 45, passes through valve 45, valve 41, through line 48, into evaporator crystallizer 25, operated at a pressure below the pressure of crystallizer 25, where a further portion of propane is evaporated because of the reduction in operating pressure, through line 49, separator 50, line 5I, valve 52, to propane The chilled solution is withdrawn from evaporator crystallizer 25 through line 53 which is controlled by valve 54 and passes through valve 55, valve 56, line 51, into evaporator crystallizer 21, it being understood that valves 58 and 59 are closed. When evaporator crystallizers 25 and 25 are operated in parallel, valves 55 and 45 are closed so that the chilled solution from both evaporator crystallizers 25 and 25 will pass through lines 55 and 6I into line 52, thence through line 63, through valve 59 which will be open, into evaporator crystallizer 21.

`It is understood, of course, that in evaporator crystallizer 26, further light gas from light gas main 39 may be passed through line 64 which is controlled by valve 65 into evaporator crystallizer 26 in order to reduce the partial pressure of the propane therein, permitting a greater evaporation thereof, thus obtaining a lower temperature under the given operating pressure. In evaporator crystallizer 21, operated at a pressure below the pressure of evaporator crystallizer 26, further propane is evaporated from the solution through line 66, separator 61, line 68, valve 59, to exhaust propane main 38. At the same time, light gas from light gas main `39 will pass through line 1I) which is controlled by valve 1I, into evaporator crystallizer 21` to permit Daltons law to operate,

vobtaining a further reduction in temperature without a corresponding reduction in pressure. Alternately it is to be understood that the light gas may be injected into the solution before the solution is introduced into each of the evaporator crystallizers 26 and 21. The chilled solution, which by this time is minus 50 F. for example, is withdrawn from the bottom of evaporator crystallizer 21 through line 12 which is controlled by valve 13 and passes through line 14, through valve 15, valves 16 and 11 to filter feed tanks 18 and 19. Filter feed tanks 18 and 19 are equipped with lines and 8|, controlled by valves 82 and 83, communicating with low pressure propane main 38 through respective separators 84 and 85. Either feed tank may be employed, or both may be used simultaneously.' The solution in filter feed tanks will contain chiefly the oil, While the wax will be present in precipitated form. The oil diluent solution containing the wax in precipitated form is withdrawn from filter feed tanks 18 and 19 through line 86, Where it passes through lines 81, 88 and 89 to be pumped by respective pumps 90, 9|, 92, through respective filters 93, 94 and 95. The wax diluent mixture leaves the filters 93, 94, and through respective mixers 96, 91, and 98, which serve to keep the wax in liquid slurry form to prevent clogging of line 99 through which the wax diluent mixture passes into petrolatum diluent mixture tank |00. The admixed oil diluent solution filtrate passes through line I0| to the wax free oil solution storage tank |6, whence it passes through line |8, through the heat exchanger bank I5 as hereinbefore described.

Storage tank |6 is provided with a vent pipe |02 and storage tank |00 is provided with a vent pipe |03, allowing such propane as is evaporated by an increase in temperature to escape.

The dewaxed oil solution from line I9 passes into pressure stabilizer 20 in which it is reboiled. The bottom |04 of stabilizer 20 divides the tower into two compartments. The incoming oil diluent solution accumulates upon bottom |04 and is picked up by pump |05 and circulated through reboiler |06 to which any suitable heating medium may be supplied, such as steam or hot oil from any refinery operation, and discharged through line |01 back into the pressure stabilizer 20. The propane is thus driven ofi and passes into main |03. The wax diluent mixture and/ or solution, is withdrawn from tank |00 through line |09, which is controlled by valve ||0, and passes through a heater which serves to drive the wax into solution and/or render it sufficiently fluid to be handled in a pipe line. Any suitable heating medium may be passed through heater through port ||2 and out of port II3. The heated wax diluent solution passes through line ||4 which is controlled by valve I|5, into pressure stabilizer |6, which is equipped with a bottom partition ||1 similar to partition |04 of pressure stabilizer 20. Pump ||8 circulates the wax diluent solution through reboiler II9, which is supplied by heating medium through port |20, and the heated wax diluent solution is reinjected into the tower through line |2|, which is controlled by valve |22. It will be readily appreciated that in'respective pressure stabilizers ||6 and 20, the diluent gas will be driven off. The gas from pressure stabilizer ||6 will pass through line |23, which is controlled by valve |24, into line I 08 from which the combined gases pass through line |25, through condenser |26, which is supplied by any suitable cooling medium, through line |21, and leaves condenser V|26 through line |28. The cooled gases from condenser |26 pass through line |29, which is controlled by valve |30, into receiver |3I. A portion of the liquefied gas from receiver |3| is pumped by pump |32 through line |33, which is controlled by valve |34, through lines |35 and |36 as reflux to the pressure stabilizers 20 and I I6. The lighter uncondensed gases pass from the receiver |3| through line |31, which is controlled by valve |38, into the light gas main 39, or into collecting main 38. Propane from the bottom of receiver |3| passes through line |39 which is controlled by valve |40, through line I4 I, which is controlled by valve |42, through line |43 into condenser |44, which is supplied with cooling medium entering through pipe |45 and leaving through pipe |4517., through line |46, into accumulator tank |41, whence it passes through line |48 to the propane tank 5.

The denuded, dewaxed oil from the upper portion of pressure stabilizer 20 passes through line |50, which is controlled by valve |5|, into the lower portion |52 of the pressure stabilizer. This lower portion is virtually a separate chamber. A steam pipe |53 which is controlled by valve |54, discharges steam into chamber |52 in order to strip the last traces of propane from the dewaxed oil. The dewaxed oil is then Withdrawn through line |55 which is controlled by valve |56, and pumped by pump |51 through line |58 to storage. The petrolatum which is sufficiently hot to be handled in a pipe line, is withdrawn from the upper portion of pressure stabilizer ||6 through line |60, which is controlled by valve |6I, into chamber |62, which is virtually a separate chamber. Steam through pipe |53, which is controlled by valve |64, is injected into chamber |62 to denude the Wax from any last traces of propane. The wax is withdrawn from the bottom of chamber |62 through line |65, which is controlled by valve I 66 and is pumped by pump |61 through line |68 to petrolatum storage.

Line |10 communicates with the upper portion of chamber |52 and is controlled by valve |1|. It passes from chamber |52 to line |90. Pipe |80 communicates with chamber |62 and is controlled by valve I8| and passes, together with line |10, to line |90, which communicates with barometric condenser |9|. The vacuum will insure the removal of all last traces of gas in both the oil and the Wax. The gas is discharged from the barometric condenser |9| through line |92. It will be observed that low pressure propane collecting main 38 communicates with line 200 which passes to suction tank 20 I, together with the vent line |02 from the wax free oil solution tank I6.

Compressor 202 takes suction through line 203 to y suction tank 20|, compresses the propane and passes it into receiver 204, whence it leaves through line 206 and passes, together with the propane in line |39 through line 4|, through condenser |44 to accumulator |41. The uncondensed gases from accumulator |41 will be the light gases which are passed from accumulator |41 through line 201 to the light gas main 39. It will be observed that the accumulator is at once a separator, substantially separating the heavier gases, which will liquefy at comparatively mild temperature and pressure, from the lighter gases so that we can reuse both the propane fractions `and the gaseous fractions. lBoth fractions, of course, are under the same pressure on again entering the system for reuse. If desired, the gaseous fractions may be rejected from the system through line 201a controlled by valve 20117.

In event it be desirable to supply further light gases to the system. these may be lniected through line 300 which is controlled by valve 30|, it being understood of course that the light gases are under pressure and may be obtained from any suitable source such as from previous refinery operations or from natural gas. above, ammonia or other non-hydrocarbon gases may be employed if desired.

Inasmuch yas the pressure may be suiiiciently highland the temperature'may be suiciently low in cooler |44 so that many lighter gases will be liquefied and passed to propane tank 5, we may further our processes in another manner, namely as follows:

`A solution of the `diluent and the liqueed gases is formed as before. In this connection, it might be Well to note that only the lighter gases may be either diluent or non-diluent gas, while the heavier gases arealways solvent gases. It is only necessary that suiiicient liquid gases be present to act as a diluent solvent. Y Upon being precooled and arriving at evaporator crystallizer25, the "pressure is reduced as before, but valve 34 is closed and valve 3'6 is open.,V The rst `reduction of pressure will allow the lighter 'constituents to evaporate. These will pass through line 400 which is controlled by valve 36,' into line 64, in whichvalve 65 is closed, and thus into evaporator crystallizer 26. Similarly, areduction of pressure inV evaporator crystallizer 26 will allow further of the lighter gases to evaporate and valve52 beingclcsed, and valve 40| being opened, the lighterfgases will pass through line `402 into line 10, it being understood that valve 1| is closed, and thence into evaporator crystallizer 21, whence all of the light gases will pass 4through line 68 into exhaust gas main 38. The

`cy'cle is repeatedv as before, the gases being cooled Y and compressed in order to liquefy them.

A In the event that it is not desirable to operate with a closed cycle for the light gas, as previously described, an'alternate operation may be used as follows:

No'light'gas would enter the system through line 300 as'valve 30| would be closed and the `light gas would pass into the 'light gas main 39 `through line 403, controlled by valve'404. The

4injection of light gasfrom main 39 into any or all ofcrystallizers 25, 26 and 21 may be accomplished through respective lines, as' outlined heretofore. The injected gas and evaporated dilllentriwill leave each evaporator crystallizer 4throughY respective" separators. The cross connecting lines between evaporator crystallizers controlled by valves 36 and 40|A would be closed off, as wellras valves34, 52 and 69 inthe respective lines leading tof discharge main 38. Thus, the gases and vapors, leaving evaporator crystallizer 25, will pass through line 405 which is controlled by valve 406, into discharge main 401, and be rejected `from the system.` Similarly; gases and vapors from evaporator crystallizers -26`fand 21 may be-'directed to line 401. With these connections, it is possible to inject light gas into any one or all evaporator crystallizers and reject or recycle the gases and vapors from any evaporator crystallizer, as desired.

AHFor example, it may be desirous to maintain the evaporated diluent free from light gases for the purpose of -recycling the diluent. Thus, vaporized diluent inevaporator crystallizers 25 and 26rmay be passed directly to line 38, then through compressor 202, cooler |44 and, after condensation,` into propane tank 5. These crystallizers may be operated at super-atmospheric pressure, aswell as evaporator crystallizer 21. The final As pointed out temperature lowering of the solution may be accomplished in evaporator crystallizer 21 by the use of light gas to eff-ectv the greater evaporation of propane. In this case, the gases and vapors from evaporator crystallizer 21 would pass through line 4|0, controlled by valve 4| l, into line 401 for rejection. Thus, the `vaporized dluent in evaporator vcrystallizers 25 and 25 may be recycled Without contamination of light gases. The loss of diluent through vaporization `in evaporator crystallizer 21 may be made up by addition from an outside source to propane tank 5. It is understood that combinations and sub-combinations of this system of recycling and rejecting gases may readily be made.

It may be desirable to operate all the evaporator-crystallizers at super-atmospheric pressure to prevent vapor lock in pumps caused by boiling at reduced pressures and temperatures. The chilled oil-propane solution from line 2| is introduced under pressure through the line 23 and valve 28 into the evaporator-crystallizer 25 where a pressure substantially above atmospheric is maintained by suitable control of the valves 28 and 34 and propane is permitted tov evaporate to eifect a chilling of the solution. The chilled solution is transferred from this first stage crystallizer to the next stage 25 and into this stage a light gas such as methane, or ethane, is introduced from the line 54 and allowed to vent through the line 5I at a pressure slightly lower ,21 `where a pressure slightly lower than that in 'either of the other stages' 25--26 `is maintained. A light gas is again introduced through the line and equilibrium conditions established by evaporation with the attendant reduction in temperature. It is to be observed that the light gas may be introduced, if desired, into the solution before the solution enters the evaporator-crystallizers 26 and 21. The oil solution after de- Waxing may be relieved of its light gas content by introduction into a ash tower (not shown) in the line I9. the top of the tower may be returned to the light gas main 30 while the bottoms of the tower are redirected into the line I9 for passage to still 20. In operation, it may be seen that there are thus threemethods of operation possible with the system.

First, anoil propane solution which has been precooled to a temperature of about 40 F. is pumped through line 2| at a pressure of around 100 lbs. to the evaporator crystallizer 25. 'I'he solution under these conditions will be in equilibrium. The solution on being injected into the evaporator crystallizer 25 is reduced in pressure by suitable control of the valve 28 and adjustment of the back pressure by control ofthe valve 34 in the line 33 until a pressure of around 25 lbs. gauge is arrived at in the evaporator crystallizer 25. Propane will evaporate from the solution with an attendant reduction inv vtemperature` until equilibriumV conditions are again established. 'I'he temperature of thesolution will now be around 10 F. The solution may now be transferred under its own pressure through valve 45, line 44, valve 46, valve 41 and line 48 to the evaporatorcrystallizer 26 where by suitable manipulation The isolated light gases from of the Valve 4l and valve 52 in line 5l a further reduction in pressure may be achieved and a further reduction in temperature had by propane evaporation. This procedure may be repeated until the desired low temperature is arrived at, at which time, the pressure will have fallen to atmospheric or sub-atmospheric pressure with the attendant diiculty of pumping the chilled solution to the separating units.

Secondly, an cil propane solution in line 2l at a pressure of about 100 lbs. gauge and at a temperature of about 40 F. is injected into the evaporator crystallizer 25 where the pressure is reduced 4to about 25 lbs. gauge by suitable control of the valves 28 and 45. Propane will then evaporate until equilibrium conditions are established and the temperature is reduced to 10 F. as before. A lighter gas is then introduced through the line 4l and due to the partial pressure effect of the light gas, a further reduction in temperature to 5 F. will be effected without further decrease in pressure. The chilled solution will then be transferred under its own pressure as before to the evaporator crystallizer 25. A further reduction in pressure here will permit more propane to evaporate and the temperature will be further reduced. A light gas will again be introduced through line 64 to effect further temperature reduction without a decrease in pressure by operation of Daltons law. This process may be continued until the desired low temperature is reached.

Thirdly, the oil propane solution at 100 lbs. gauge pressure and a temperature of 40 F. is introduced from line 2| into the evaporatorcrystallizer 25 and the pressure reduced to about 30 lbs. gauge by proper manipulation of valves 28 and 34. Propane is permitted to evaporate until equilibrium is restored. The cooled liqui-d is then transferred to the evaporator-crystallizer 26 where the pressure is only slightly lowered from that in evaporator crystallizer 25 by manipulation of valves 41 and 52. A light gas is then injected through line 54 and a further reduction of temperature eiected as a result of the operation of Daltons law. By introducing the lighter gas at the lower temperature and pressure, a certain percentage of these compounds Will be condensed and retained in the chilled solution, Whereas if the liqueed hy-drocarbon consisting mainly of propane, had contained even considerable quantities of these light materials in the original blend, they would have been flashed 01T inthe rst evaporator-crystallizer 25. The solution will be reduced in temperature in the evaporator-crystallizer 26 to about +5 F. It is tobe observed that the low temperature secured by the evaporation of propane and a light gas at the lower pressure as in case two is not had in the instant case because of the higher pressure existing in the evaporator crystallizer 26. This disadvantage is offset by the helpful eiect of the greater pressure in preventing or minimizing boiling of the solution in its passage through the pumps to the separating units. The process also has the added `advantage that less propane is required to effect the desired low temperature than would be required if propane alone Were used at the lower pressures.

It is believed that the operation will be clear from the above description. It will be seen that we have accomplished the objects of our invention. We are enabled to chill solutions to a lower temperature for a given pressure by the introduction of a light gas into any single one or a plurality of the evaporation zones. We are enabled to chill solutions or mixtures which are at equilibrium or which are under a pressure which is greater than the equilibrium pressure for a given temperature. Under ordinary conditions or equilibrium no evaporation with attendant chilling would take place. Under our method, we accomplish chilling by the introduction of a light gas. We are enabled to maintain favorable crystallization conditions by avoiding an undesirable excess of diluent which would interfere with favorable crystal growth. At the same time we are enabled to reduce the amount of material to be chilled, thus reducing the refrigeration load and the chilling time interval.

It will be understood that certain features and sub-combinations are of utility and may be employed Without reference to other features and sub-combinations. This is contemplated by and is Within the scope of our claims. It is further obvious thatv various changes may be made in details within'the scope of our claims without departing from the spirit of our invention. It is, therefore, to' be understood that our invention is not toy be limited to the specic details shown and described.

Having thus described our invention, what we claim is:

1. A method of dewaxing hydrocarbon oils including the steps of dissolving a hydrocarbon oil in a liquefied, normally gaseous solvent, cooling the solution by evaporating a portion of the solvent by reducing the pressure on the solution, obtaining a further decrease in temperature of the solution Without a further reduction in pressure thereon by introducing a gas of lower boiling point than the solvent gas into the 4cooling zone to permit an operation of Daltons law whereby the desired Wax precipitating temperature is obtained, permitting wax to precipitate and separating precipitated wax from the solution.

2. A method of dewaxing hydrocarbon oils including the steps of dissolving a hydrocarbon oil in a mixture of liquefied gases of progressively lower boiling points, said mixture containing a component capable of dissolving wax-bearing hydrocarbon oil, reducing the temperature of the solution in a first cooling zone by reducing the pressure on the solution sufficiently to permit evaporation of the lighter gases of the mixture, further cooling the solution in a second cooling zone by evaporating a portion of the heavier gases of the mixture by further reducing the pressure and obtaining a further reduction of temperature of the solution without a further reduction of pressure thereon by introducing the gases evaporated from the first cooling zone into the second coo-ling Vzone to permit an operation of Daltons law whereby the desired Wax precipitating temperature is obtained in the solution, permitting wax to precipitate and separating precipitated wax from the solution.

3. A method of dewaxing hydrocarbon oils including the steps of dissolving a wax-bearing hydrocarbon oil in a liqueed normally gaseous solvent, cooling the solution in a first cooling zone by reducing the pressure on the solution sufliciently to evaporate a portion of the solvent, obtaining a further decrease in temperature without a further'decrease in the pressure on the solution by introducing a gas of lower boiling point than the solvent gas into said cooling zone, passing the cooled solution by means of the gas pressure thereon into a second cooling zone,

there further reducing the pressure on the solution to obtain another reduction in temperature of the solution and introducing a gas of a lower boiling point than the solvent gas into the second cooling zone to obtain a. further decrease in temperature of the solution Without a further decrease in pressure thereon and by the process obtaining the desired wax precipitating temperature, permitting Wax to precipitate and separating precipitated Wax from the solution.

4. A process as in claim 1 wherein the gases freed from the cooling step are compressed and cooled at such temperature and pressure that a portion of the lighter gases are left-in the gaseous state while most of the heavier gases are liquefied.

5. A method of dewaxing hydrocarbon oils including the steps of mixing a Wax-bearing oil with a liquelied normally gaseous diluent, evaporating a portion of the diluent to chill the solution by reducing the pressure thereon, increasing the extent of the evaporation by introducing a lower boiling gas into the evaporating zone to reduce the partial pressure therein, the process being such that the amount of diluent added in the mixing though maintaining a'desirable concentration of diluent lduring the chilling step is less than that amount which would be required to cause sufficient evaporation to give the desired low temperature in the solution if the light gas were not used, whereby the refrigeration load is decreased and excess of diluent during the chilling step is avoided, permitting wax to precipitate and separating precipitated wax from the solution.

6. A method of dewaxing hydrocarbon oils inciu-ding the steps of mixing a wax-bearing oil with a liqueed normally gaseous diluent, reducing the pressure on the solution thereby evaporating a portion of the diluent by its own partial pressure to chill the solution in a first chilling step, transferring the chilled solution to a second chilling zone, further reducing the pressure on the solution and injecting a lower boiling gas into the second chilling zone thereby evaporating a further portion of the diluent under the partial pressure of the lighter gas in the second chilllhg step to further chill the solution and precipitate the wax, and separating the precipitated wax from the solution.

EARL PETTY. KARL FINSTERBUSCH. 

